The present invention relates to a color display device for displaying images, a liquid crystal display (LCD) device, and a semi-transmissive LCD device.
Currently available color display devices for use in practical applications include devices based on various kinds of display technologies, such as cathode ray tube (CRT) monitors, liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light-emitting diode (LED) panels, field emission display (FED) panels, and electrophoresis or electrochrominance-based electronic paper (“e-paper”) display panels. A major approach to achieving color image displaying in non-emissive LCDs is to use a technique for arranging a picture element or “pixel” by a parallel layout of sub-pixels having color filters of the three primary colors, i.e., red (R), green (G) and blue (B), and for adjusting the brightness of each subpixel independently of one another to thereby represent any given color by additive color mixture methods. Another approach for use with emissive displays is to arrange a pixel by parallel layout of subpixels having fluorescent materials of the three primary colors, i.e., red (R), green (G) and blue (B), and for adjusting the brightness on a per-subpixel basis in a similar way to LCDs to thereby represent any given color by additive color mixture methods in a similar way to LCDs.
In the case of the technique for performing color displaying by additive color mixture with the use of three-primary-color subpixels, it is possible to display on-screen images in vivid colors with high fidelity; on the contrary, as the area of each primary color-allocated subpixel is one third (⅓) the total area of a pixel, the resulting efficiency stays less, posing a problem as to deficiency of light amount.
One solution to this problem is to employ an arrangement with addition of subpixels of white (W) color, as proposed and disclosed in JP-A-11-295717. In the white (W) subpixels used in non-emissive LCDs, there is no light absorption at color filters so that it is possible to enhance the use efficiency of a light source. As the white (W) subpixels in emissive ones is high in brightness per unit area, it is easy to increase the brightness of display device.
In the case of adding the white (W) subpixels, if these subpixels are simply added, there exists a penalty as to unwanted increase in number of signal transmission lines and/or scanning lines. A pixel configuration with the white (W) subpixels being added thereto without having to increase the number of such lines is disclosed, for example, in U.S. Patent Application Publication No. 2005/0225575 A1.
Another problem of the additive color mixture-based color display scheme with the parallel layout of three-primary-color subpixels is that the color reproduction range is limited to within the zone of a triangle determined by chromaticity coordinate points of the three primary colors, resulting in a region being left widely, which is incapable of reproducing most of the real colors in the natural world. To solve this problem, an attempt is made to lay out subpixels of four primary colors to thereby expand the color reproduction range from the triangle to a rectangle.
An example of such four-primary-color display device is found in JP-A-2005-338783.